The optical disks generally available on the market today can be broadly classified into dye-type disks that create marks by changing locally the chemical composition or optical characteristic of the recording film principally made of a pigment or pigments by heating the same, magneto-optical disk that create marks by inverted magnetic domain on the recording film resulting from heating the perpendicular magnetic recording film and phase change disks that create marks by amorphous domain on the recording medium by changing the peak temperature at the time of heating the recording film and cooling speed by controlling the amount of energy inputted at the time of heating. The means of improving the information transfer speed during the time of recording or reproduction on these optical disks includes increasing recording linear density or increasing the scanning speed of the recording medium by light spot. The means of increasing the recording linear density includes the direct method of scaling down marks and space length themselves, the method of reducing the unit of change in the length of symbols (marks and spaces) and thus reducing the length of time for detecting the mark edge position. However, in any of these means of increasing recording linear density, the deterioration of signal-to-noise ratio in the regenerative signals proves to be a problem, and in the present technical condition it is hopeless to expect any improvement in information transfer speed by improving recording linear density.
For the purpose of forming high-precision and miniscule marks on an optical disk and improving recording linear density, according to the first prior art described in JP-A No. 298737/1993, the method of forming the recording waveform corresponding to the mark-forming period from a series of pulse sequences corresponding to the mark length of the recording data sequence and controlling the number and amplitude of each pulse according to the length of the recording data sequence has been disclosed. The recording waveform of the mark-forming period is divided into two parts: the top part and the succeeding part, and the pulse height of each pulse is generally different. In addition, during the mark non-forming period of a recording waveform, after the preposition of a space part, recording auxiliary pulses for preheating the recording medium are generated. By the method described above, according to the first prior art publication document, the heat diffusion from the preceding mark-forming part to the immediately following the leading edge position of the mark can be supplemented not by the space length, the mark width and the mark edge position can be controlled very precisely, and as a result recording linear density can be improved. Here, the mark-forming period is defined as the period from the first pulse rise to the last pulse fall of the pulses having an energy level for supplying recording energy necessary for forming a single mark, in other words the pulses having an energy level without the generation of which no mark is formed, by reflecting the mark length in the recording data sequence as shown in FIG. 3. And the mark non-forming period is defined as the period other than the mark-forming period reflecting the length of space in recording data sequence. The definitions given above shall be common in the description of the present Specification.
The second prior art described in JP-A No. 7277/1996 discloses a method of breaking up each recording data into a plurality of basic elements of different length, correlating each element to a single recording pulse, and forming a series of recording marks as a succession of respectively independent recording marks by each recording pulse. The second prior art publication document describes that no decline in the level of reproduce signals results from the recording of independent marks by this method in the middle of any marks and that stable recording can be maintained even by the modulation method including long marks. It further states that on rewrite-type recording medium, it is possible to contain any increase in jitter of regenerative signals after a large number of rewriting and as a result it is possible to improve recording linear density.
In addition, the third prior art described in JP-A No. 134525/1997 discloses a method that, in the case of recording of either one of even mark length or odd mark length for the recording channel clock cycle in the multi-pulse recording method including the top heating pulse, the succeeding plural rear heating pulses, the rear cooling pulses and the final tail cooling pulse, the method of bringing the pulse length of the rear heating pulse and the rear cooling pulse to almost the same as the recording channel clock cycle. The third prior art publication document discloses that this method can secure a sufficient cooling time of the recording medium, enables to control precisely the edge position and consequently to increase the information recording speed at the time of recording by improving recording linear density.
The fourth prior art described in JP-A No. 175976/1999 discloses an information recording apparatus for recording information by injecting energy on the recording medium and by forming marks of different physical characteristic from that of the unrecorded part including an encoder for converting information into recording data sequences, a means for classifying marks natural number n times long of the detection window width according to the remainder remaining after dividing n by an integer constant of 2 or more by referring to the length of marks in the recording data sequence, an energy generator for generating the energy necessary for recording, and the driver of the energy generator for changing the pulse number of the injected energy in the mark-forming period depending on the length of marks in the recording data sequence, wherein the driver is a means for driving the energy generator according to the different procedure based on the result of classification of the classifier. As the fourth prior art enables to secure sufficient cooling time of the recording medium or to reduce the frequency spectrum of the laser driving current, it will be possible to form marks with a sufficient precision even during a high-speed information recording, and to secure both a sufficient recording linear density and reliability.
And the fifth prior art described in JP-A No. 331936/2001 discloses an information recording apparatus that, for recording mark length modulated information with a plurality of recording mark lengths on the recording medium, (i) divides the time length nT of recording mark in the order of η1T, α1T, β1T, α2T, β2T, . . . , αiT, βiT, . . . , αmT, βmT, η2T, irradiates a recording beam of a recording power Pwi within the time span of αiT (1≦i≦m), and irradiates a recording beam of a bias power Pbi meeting the requirements of Pbi<Pwi and Pbi<Pwi+1 within the time span of βiT(1≦i≦m), and (ii), depending on n of time length nT of the above-mentioned recording mark, renders m, αi, βi, η1, η2, Pwi and Pbi variable, sets the number of division of the pulse m at 2 or more for the time length of at least one recording mark, and sets the time length of all the recording marks at a value meeting the requirement of n/m≧1.25. It was disclosed that this fifth prior art enables to provide an optical recording method resulting in good recording made even in the case of mark length recording at a short clock cycle suitable for a high-density recording or a high-speed recording.